As the development of bubble jet devices has progressed, two general categories of drop ejection approach have evolved: (i) ejecting drops in a direction generally parllel to the surfaces of the heater elements and their electrical circuitry and (ii) ejecting drops in a direction generally normal to the heater element surfaces. U.S. Pat. No. 4,330,787 describes several advantages of the latter category of devices, herein termed "normal drop ejector" devices.
Another way in which such bubble jet devices can be catorgorized is as to whether the print head has a remote ink supply reservoir, coupled to the print head by an umbilical, or has an attached ink supply. In the latter category of devices the print head and ink supply form a print/cartridge which can be transversed within the printer as a unit and the print/cartridge or its ink container component is replaced when the ink is exhausted. The remote and attached ink supply approaches each has its own advantages, for different printer embodiments. For example, the removable print/cartridge approach is desireable for small, portable printers and a large number of different configurations have been devised for print/cartridge devices.
As can be noted for example in U.S. Pat. Nos. 4,567,493; 4,500,895; 4,680,859 and 4,771,295, the typical approach for providing ink passage from the ink reservoir of a print/cartridge to the drop ejection zone, is by forming an openings, e.g. holes or slots, through the driver chip on which the heater elements and leads are formed. This approach works particularly well for "normal drop ejector" devices because the ink reservoir can then be located on the opposite side of the driver chip from the orifice plate and printing zone.
However, the forming of openings through the driver chip presents some difficulties. First, this necessitates an additional fabrication step which is time consuming and can itself damage the fragile chip substrates. Second, the existence of slots or holes through the chip weaken its structural integrity and can result in breaking or cracking during subsequent assembly steps of the print/cartridge fabrication. Also, such openings occupy a portion of the chip operative surface area.